1. Field of the Invention
This invention relates to a plug-in unit-mounting structure for mounting plug-in units each having various circuit packages mounted on a printed board thereof, and an electronic apparatus, and more particularly to a plug-in unit-mounting structure of a bookshelf-type electronic apparatus for removably mounting plug-in units.
2. Description of the Related Art
Electronic apparatuses for communication, such as transmitters and switchboards, use a bookshelf-type electronic apparatus in which a plurality of printed board units (hereinafter referred to as “PIUs”) each comprised of electronic circuit packages are vertically mounted on a back wiring board (BWB) mounted on the rear face of a metal shelf thereof. The PIU is comprised of a printed wiring board and a plurality of electronic circuit packages each formed with electronic circuits, such as LSIs, mounted on the printed wiring board. There have been already proposed several plug-in unit-mounting techniques for mounting plug-in units on the BWB.
FIG. 10 is a front view of an example of a conventional plug-in unit-mounting structure.
In the illustrated example, pairs of substantially C-shaped guide rails 103a and 103b are secured to a metal shelf 100 at respective locations of upper and lower sides 101 and 102 of the metal shelf 100 at equal space intervals in a manner opposed to each other. Box-shaped full-size PIUs 104 can be vertically mounted in the metal shelf 100 using the guide rails 103a and 103b as guides. Further, by providing an intermediate guide member between the upper guide rail 103a and the lower guide rail 103b in the metal shelf 100, and attaching a center rail 105 to the intermediate guide member, it is possible to mount a half-size box-shaped PIU 106 at an upper shelf using the center rail 105 and the upper guide rail 103a as guides. Further, a half-size PIU 107 can be mounted at a lower shelf between the lower guide rail 103b and the center rail 105, by causing the rails as guides.
Therefore, PIUs 104 and 106 having various sizes can be mounted on the back wiring board of the metal shelf 100 shown in FIG. 10, and hence it is possible to simplify the design of e.g. a package-type communication apparatus, which improves not only economy but also the convenience of maintenance. It should be noted that a description of such a communication apparatus and a plug-in unit is given e.g. in International Publication Number WO 00/074454 (Section of “Outline of Construction of Communication Apparatus 10” in Detailed Description, and FIG. 1).
FIG. 11 is a front view of another example of the plug-in unit-mounting structure.
In the illustrated example, substantially C-shaped guide rails 202 are mounted on a wiring board 201 of a metal shelf 200 in a cantilever manner such that they protrude forward and are inwardly opposed to each other. The vertical distances between locations where the guide rails 202 are mounted are determined in a manner adapted to respective PIUs to be mounted on the back wiring board 201, e.g. a full-size PIU 203 and a half-size PIU 204. The PIUs 203 and 204, which are both box-shaped, have bar-shaped guides (not shown) mounted along two opposed sides which are orthogonal to sides where connectors are mounted, whereby the PIUs 203 and 204 are guided by the guide rails 202.
A description of such a printed board unit-holding structure of electronic units is given e.g. in Japanese Laid-Open Patent Publication No. 04-113693 (fourth and fifth pages, and FIGS. 1 and 3). When mounting printed board units having different sizes, they are formed as the box-shaped PIUs 203 and 204, and are mounted using the guide rails 202 attached to the back wiring board 201 according to the respective heights of the PIUs 203 and 204. This is advantageous in that the printed board units can be mounted in high density without the waste of space.
FIG. 12 is a front view of another example of the plug-in unit-mounting structure.
In this plug-in unit-mounting structure, substantially C-shaped guide rails 303a and 303b are fixed to an upper side 301 and a lower side 302 of a metal shelf 300 in a manner opposed to each other, and printed board-type full-size PIUs 304 are mounted using the guide rails 303a and 303b as guides. Further, some of the guide rails 303a and 303b fixed to the metal shelf 300 hold printed board unit-mounting frames 305. Each mounting frame 305 has center rails 305a and 305b integrally formed therewith, and grooves 305c formed in the top and bottom thereof, for engagement with the guide rails 303a and 303b (e.g. Japanese Laid-Open Patent Publication (Kokai) No. 2005-277281 (Paragraph Numbers [0010] to [0024] and FIG. 1)).
By using the printed board unit-mounting frame 305, a half-size PIU 306 of printed board type is mounted at an upper shelf by being guided between the guide rail 303a and the center rail 305a of the printed board unit-mounting frame 305, and another half-size PIU 306 of printed board type is also mounted on a lower shelf by being guided between the guide rail 303b and the center rail 305b of the printed board unit-mounting frame 305.
In the illustrated example, only by fixing the guide rails 303a and 303b to opposed sides of the metal shelf 300, it is possible to cope with plug-in units having different sizes. Therefore, as distinct from the case of the metal shelf 100 shown in FIG. 10, it is not necessary to provide the intermediate guide member and attach the center rail 105 thereto, which makes it possible to perform high-density mounting using a smaller number of components. Further, as distinct from the metal shelf 200 shown in FIG. 11, it is not required to mount the guide rail 202 on the back wiring board 201 in a manner adapted to the size of a printed board unit. Therefore, even when a printed board unit already mounted in the metal shelf 300 is replaced by a printed board unit having a different size, it is possible to easily mount a printed board unit having a desired width at a predetermined location.
However, in both of the FIG. 10 and FIG. 12 examples of the conventional printed board unit-mounting structure, described above, the guide rails for guiding the PIUs are mounted on the metal shelves 100 and 300 per se. In general, the number of layers of a printed circuit board increases or decreases depending on the amount of wiring, and hence as the amount of wiring becomes larger, the thickness of the printed circuit board inevitably tends to increase. On the other hand, when the upper and lower sides of a plug-in unit (PIU) are held by the guide rails 303a and 303b, the width of the guide rails corresponds to the thickness of the printed circuit board, and hence it is difficult to replace the printed circuit board (PCB) in use with a printed circuit board having a larger amount of wiring and hence having a different thickness.
More specifically, the guide mechanism (guide rails 103a and 103b) for mounting the box-shaped PIUs 104 and 106, described hereinabove with reference to FIG. 10, is configured to be integrally formed with the metal shelf 100. Therefore, there is a problem that the thickness of PIUs that can be mounted in slots is fixed.
Further, in the case of the metal shelf 300 for having the PIUs 304 and 306 of printed board type mounted therein, shown in FIG. 12, the substantially C-shaped guide rails 303a and 303b fixed to the upper and lower sides 301 and 302 in a manner opposed to each other are used, and hence if a plug-in unit has a different thickness, as in the case of a plug-in unit in which a heat sink provided with a radiation fin is arranged on a PCB, it is difficult to mount the plug-in unit. What is more, when mounting a box-shaped PIU without containing a PCB, it is required, to begin with, to provide guide rails for guiding the box-shaped PIU, in place of the fixed guide rails 303a and 303b. 
On the other hand, the FIG. 11 metal shelf 200 for mounting the box-shaped PIUs 203 and 204 is adapted only to the box-shaped PIUs 203 and 204, and hence it is impossible to mount plug-in units having a printed board exposed without being covered with a box-shaped covering. Further, since the opposed guide rails 202 are separately fixed to the back wiring board 201, and hence, the distance between the opposed guide rails is sometimes not uniform due to variations of parts thereof.
As described above, the conventional electronic apparatuses suffer from the problem that it is not easy to replace PIUs mounted on a shelf or increase or reduce the number of mounting frames e.g. when changing the design of the apparatuses.